Commit message: hfsplus: check read_mapping_page() return value

While testing more corrupted images with hfsplus, i came across
one which triggered the following bug:

[15840.675016] BUG: unable to handle kernel paging request at fffffffb
[15840.675016] IP: [<c0116a4f>] kmap+0x15/0x56
[15840.675016] *pde = 00008067 *pte = 00000000
[15840.675016] Oops: 0000 [#1] PREEMPT DEBUG_PAGEALLOC
[15840.675016] Modules linked in:
[15840.675016]
[15840.675016] Pid: 11575, comm: ln Not tainted (2.6.27-rc4-00123-gd3ee1b4-dirty #29)
[15840.675016] EIP: 0060:[<c0116a4f>] EFLAGS: 00010202 CPU: 0
[15840.675016] EIP is at kmap+0x15/0x56
[15840.675016] EAX: 00000246 EBX: fffffffb ECX: 00000000 EDX: cab919c0
[15840.675016] ESI: 000007dd EDI: cab0bcf4 EBP: cab0bc98 ESP: cab0bc94
[15840.675016]  DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 0068
[15840.675016] Process ln (pid: 11575, ti=cab0b000 task=cab919c0 task.ti=cab0b000)
[15840.675016] Stack: 00000000 cab0bcdc c0231cfb 00000000 cab0bce0 00000800 ca9290c0 fffffffb
[15840.675016]        cab145d0 cab919c0 cab15998 22222222 22222222 22222222 00000001 cab15960
[15840.675016]        000007dd cab0bcf4 cab0bd04 c022cb3a cab0bcf4 cab15a6c ca9290c0 00000000
[15840.675016] Call Trace:
[15840.675016]  [<c0231cfb>] ? hfsplus_block_allocate+0x6f/0x2d3
[15840.675016]  [<c022cb3a>] ? hfsplus_file_extend+0xc4/0x1db
[15840.675016]  [<c022ce41>] ? hfsplus_get_block+0x8c/0x19d
[15840.675016]  [<c06adde4>] ? sub_preempt_count+0x9d/0xab
[15840.675016]  [<c019ece6>] ? __block_prepare_write+0x147/0x311
[15840.675016]  [<c0161934>] ? __grab_cache_page+0x52/0x73
[15840.675016]  [<c019ef4f>] ? block_write_begin+0x79/0xd5
[15840.675016]  [<c022cdb5>] ? hfsplus_get_block+0x0/0x19d
[15840.675016]  [<c019f22a>] ? cont_write_begin+0x27f/0x2af
[15840.675016]  [<c022cdb5>] ? hfsplus_get_block+0x0/0x19d
[15840.675016]  [<c0139ebe>] ? tick_program_event+0x28/0x4c
[15840.675016]  [<c013bd35>] ? trace_hardirqs_off+0xb/0xd
[15840.675016]  [<c022b723>] ? hfsplus_write_begin+0x2d/0x32
[15840.675016]  [<c022cdb5>] ? hfsplus_get_block+0x0/0x19d
[15840.675016]  [<c0161988>] ? pagecache_write_begin+0x33/0x107
[15840.675016]  [<c01879e5>] ? __page_symlink+0x3c/0xae
[15840.675016]  [<c019ad34>] ? __mark_inode_dirty+0x12f/0x137
[15840.675016]  [<c0187a70>] ? page_symlink+0x19/0x1e
[15840.675016]  [<c022e6eb>] ? hfsplus_symlink+0x41/0xa6
[15840.675016]  [<c01886a9>] ? vfs_symlink+0x99/0x101
[15840.675016]  [<c018a2f6>] ? sys_symlinkat+0x6b/0xad
[15840.675016]  [<c018a348>] ? sys_symlink+0x10/0x12
[15840.675016]  [<c01038bd>] ? sysenter_do_call+0x12/0x31
[15840.675016]  =======================
[15840.675016] Code: 00 00 75 10 83 3d 88 2f ec c0 02 75 07 89 d0 e8 12 56 05 00 5d c3 55 ba 06 00 00 00 89 e5 53 89 c3 b8 3d eb 7e c0 e8 16 74 00 00 <8b> 03 c1 e8 1e 69 c0 d8 02 00 00 05 b8 69 8e c0 2b 80 c4 02 00
[15840.675016] EIP: [<c0116a4f>] kmap+0x15/0x56 SS:ESP 0068:cab0bc94
[15840.675016] ---[ end trace 4fea40dad6b70e5f ]---

This happens because the return value of read_mapping_page() is passed on
to kmap unchecked.  The bug is triggered after the first
read_mapping_page() in hfsplus_block_allocate(), this patch fixes all
three usages in this functions but leaves the ones further down in the
file unchanged.

Signed-off-by: Eric Sesterhenn <snakebyte@gmx.de>
Cc: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
CVE: CVE-2008-4934
CWE: CWE-20
Vulnerability description: The hfsplus_block_allocate function in fs/hfsplus/bitmap.c in the Linux kernel before 2.6.28-rc1 does not check a certain return value from the read_mapping_page function before calling kmap, which allows attackers to cause a denial of service (system crash) via a crafted hfsplus filesystem image.

Project: linux-2.6

int hfsplus_block_allocate(struct super_block *sb, u32 size, u32 offset, u32 *max)
{
	struct page *page;
	struct address_space *mapping;
	__be32 *pptr, *curr, *end;
	u32 mask, start, len, n;
	__be32 val;
	int i;

	len = *max;
	if (!len)
		return size;

	dprint(DBG_BITMAP, "block_allocate: %u,%u,%u\n", size, offset, len);
	mutex_lock(&HFSPLUS_SB(sb).alloc_file->i_mutex);
	mapping = HFSPLUS_SB(sb).alloc_file->i_mapping;
	page = read_mapping_page(mapping, offset / PAGE_CACHE_BITS, NULL);
	pptr = kmap(page);
	curr = pptr + (offset & (PAGE_CACHE_BITS - 1)) / 32;
	i = offset % 32;
	offset &= ~(PAGE_CACHE_BITS - 1);
	if ((size ^ offset) / PAGE_CACHE_BITS)
		end = pptr + PAGE_CACHE_BITS / 32;
	else
		end = pptr + ((size + 31) & (PAGE_CACHE_BITS - 1)) / 32;

	/* scan the first partial u32 for zero bits */
	val = *curr;
	if (~val) {
		n = be32_to_cpu(val);
		mask = (1U << 31) >> i;
		for (; i < 32; mask >>= 1, i++) {
			if (!(n & mask))
				goto found;
		}
	}
	curr++;

	/* scan complete u32s for the first zero bit */
	while (1) {
		while (curr < end) {
			val = *curr;
			if (~val) {
				n = be32_to_cpu(val);
				mask = 1 << 31;
				for (i = 0; i < 32; mask >>= 1, i++) {
					if (!(n & mask))
						goto found;
				}
			}
			curr++;
		}
		kunmap(page);
		offset += PAGE_CACHE_BITS;
		if (offset >= size)
			break;
		page = read_mapping_page(mapping, offset / PAGE_CACHE_BITS,
					 NULL);
		curr = pptr = kmap(page);
		if ((size ^ offset) / PAGE_CACHE_BITS)
			end = pptr + PAGE_CACHE_BITS / 32;
		else
			end = pptr + ((size + 31) & (PAGE_CACHE_BITS - 1)) / 32;
	}
	dprint(DBG_BITMAP, "bitmap full\n");
	start = size;
	goto out;

found:
	start = offset + (curr - pptr) * 32 + i;
	if (start >= size) {
		dprint(DBG_BITMAP, "bitmap full\n");
		goto out;
	}
	/* do any partial u32 at the start */
	len = min(size - start, len);
	while (1) {
		n |= mask;
		if (++i >= 32)
			break;
		mask >>= 1;
		if (!--len || n & mask)
			goto done;
	}
	if (!--len)
		goto done;
	*curr++ = cpu_to_be32(n);
	/* do full u32s */
	while (1) {
		while (curr < end) {
			n = be32_to_cpu(*curr);
			if (len < 32)
				goto last;
			if (n) {
				len = 32;
				goto last;
			}
			*curr++ = cpu_to_be32(0xffffffff);
			len -= 32;
		}
		set_page_dirty(page);
		kunmap(page);
		offset += PAGE_CACHE_BITS;
		page = read_mapping_page(mapping, offset / PAGE_CACHE_BITS,
					 NULL);
		pptr = kmap(page);
		curr = pptr;
		end = pptr + PAGE_CACHE_BITS / 32;
	}
last:
	/* do any partial u32 at end */
	mask = 1U << 31;
	for (i = 0; i < len; i++) {
		if (n & mask)
			break;
		n |= mask;
		mask >>= 1;
	}
done:
	*curr = cpu_to_be32(n);
	set_page_dirty(page);
	kunmap(page);
	*max = offset + (curr - pptr) * 32 + i - start;
	HFSPLUS_SB(sb).free_blocks -= *max;
	sb->s_dirt = 1;
	dprint(DBG_BITMAP, "-> %u,%u\n", start, *max);
out:
	mutex_unlock(&HFSPLUS_SB(sb).alloc_file->i_mutex);
	return start;
}